The present invention is directed to the disposal of waste and more particularly to a heat recovery system and a method of heat recovery and reuse for a self-contained transportable incineration apparatus.
The disposal of waste such as trees, brush, yard waste, etc. is a major concern of the municipal, commercial and private sectors. Various types of recycling equipment and techniques are in use or have been proposed to dispose of such waste, all with varying degrees of success.
One method is to transport and to bury the waste in a landfill. However, landfill sites are becoming scarce and those remaining are cost prohibitive especially in rapidly growing urban areas. In addition, even if suitable sites can be found, they are often at a distance that makes transportation costs prohibitive. Since vegetation waste makes up approximately 40% of the bulk typically buried in landfills, most large cities require that the waste be separated from conventional garbage for purposes of mulch and compost manufacture in an effort to recycle the waste.
Each year there are tens of thousands of acres of land cleared of trees, brush, etc. for development and millions of tons of yard waste (small branches, leaves, grass, etc.) produced. Reducing the amount of such waste being buried or mulched would significantly reduce the pressure on the existing landfills and delay the need for opening new landfill sites. In addition, landfills are a relatively inefficient method of recycling. Being simply buried at one site, the economic potential of the waste material is never fulfilled. Also, solid waste landfills are diminishing rapidly and permits for new sites are difficult to secure.
Another waste material that presents challenges with regard to disposal is animal carcasses. In the past, diseased animal carcasses were usually buried and forgotten. Little was known about the agents that caused the deadly diseases which have wiped out many herds of cattle and entire chicken farms. It has been discovered that certain pathogens can survive for over fifty years in the soil where they have been buried along with animal carcasses that perished from the disease.
One alternative to landfills has been to incinerate the waste material. With regard to wood and vegetation wastes, this produces an ash residue which is extremely high in natural nutrients beneficial for plant growth. When the ash is mixed with compost and varying amounts of soil, a range of products from high-grade potting soil to top soil are developed. Open burning of the vegetation waste on site is the simplest and most cost effective way of incinerating the waste material. However, due to the many environmental limitations imposed by federal, state, and local jurisdictions, open burning is not always feasible or possible. With regard to the disposal of animal carcasses, the only known practical approach to the elimination of diseased carcasses is high temperature incineration.
Some open pit incineration has been made possible through the use of air curtain incinerators such as the device disclosed in U.S. Pat. No. 4,756,258. In an open pit incinerator, the waste is loaded into a fire pit through an opening and then ignited. High velocity air from a manifold positioned along the opening is then blown over and into the pit. The air flow pattern is intended to over-oxygenate the fire for more complete combustion and to provide a rotating mass of air that acts as a barrier or curtain to reduce the emission of smoke and ash from the fire.
A drawback of open pit incineration is the need for creation of the pit. This requires the employment of an earth mover and an operator familiar with pit construction. In many instances, neither an earth mover or a qualified operator is available and timber is incinerated in an open stance. This poses additional problems in that wind gusts could cause the loss of fire control.
Another drawback to open pit incineration is that the location of the pit may not always be convenient and therefore, transportation may be required. Over the road transport of waste materials is costly and in the case of diseased animals is undesirable for many reasons.
The problems associated with open burning and fire pits are addressed in U.S. Pat. No. 5,415,113, which is assigned to the assignee of the present invention. The patent discloses a portable incineration apparatus that provides an air curtain for reducing the emission of smoke and ash and to provide for more complete combustion of the waste materials. The apparatus provides a box having four walls with a top opening and a bottom opening. The inside of the walls are lined with a layer of a refractory material to form a combustion chamber. The incinerator also includes a source of high velocity air that is in air transfer communication with a manifold assembly. The manifold assembly is adapted to direct an effective sheet or curtain of high velocity air across the top of the opening and down into the combustion chamber and to maintain a substantially uniform discharge rate of the high velocity air as it exits the manifold assembly along the top opening. The high velocity air curtain covers the top opening and creates a rotational turbulence within the combustion chamber. It has been found that because of the substantially uniform discharge rate, the resulting curtain of high velocity air over the top opening limits the amount of particulate, such as ash, released into the atmosphere during combustion and virtually eliminates opacity or smoke.
The panels that make up the side walls of the apparatus weigh up to 1200 pounds each and are constructed of refractory materials rated to withstand temperatures to 2800xc2x0 F. The temperature inside the combustion chamber approaches 2500xc2x0 F. to 2800xc2x0 F. To reach the optimum combustion temperatures as quickly as possible, the incinerator preferably includes a diesel and/or propane ignition system for igniting and fueling the combustion of the waste until these temperatures are achieved.
Given the temperatures and the amount of heat generated inside the combustion chamber of the portable incineration apparatus, there is a need for recovering and reusing some of the heat generated in the combustion chamber.
The present invention meets the above-described need by providing a heat recovery system and a method for recovering and reusing heat generated by a portable incineration apparatus.
The system provides a transportable box defined by four walls and having an open top and an open bottom. The walls are lined with a refractory material operatively associated with the open bottom to form a combustion chamber. The system also includes a source of high velocity air and a manifold for directing an effective curtain of high velocity air across the top opening and down into the combustion chamber.
The heat recovery system comprises a system of tubing for conveying a heat conductive medium through the tubing during the combustion process. The tubing may be mounted to the walls, mounted inside the walls, or formed integrally in the walls. The tubing is preferably disposed in serpentine fashion through the walls such that maximum heat transfer between the combustion chamber and the heat conducting medium occurs during the time that the medium is conveyed through the tubing. The walls are preferably divided into individual panels that are lined with a refractory material. Each panel carries an individual section of tubing having a fitting for an input and an output. Accordingly, the tubing system for the panels may be connected in series or parallel depending on the heating requirements of the specific application.
The heat conducting medium may comprise a liquid, gas or multi phase substance that may be used for many different applications. Some waste treatment sites have retention ponds with microorganisms for cleaning up the water in the retention pond. Water cycled through the tubing system of the present invention at the incinerator may be conveyed to the retention pond where the heated water provides for heating the ponds in order to optimize the activity of the microorganisms.
As an alternative, the heat conducting medium that passes through,the pipe system during combustion may be used to provide a source of convective heat for equipment or facilities located near the portable incinerator.
Also, the heat conducting medium may provide an input for manufacturing process that require a preheated liquid or gas.
Finally, it is also possible in some applications to have the pipes connected in series to produce steam for suitable steam-powered processes.